Pregnant women will be allowed to enroll irrespective of their gestational age, although they cannot enroll at delivery because they cannot undergo adequate consent. However, potential participants will be strongly encouraged to come to the clinic for prenatal care early in the second trimester (ideally <16 weeks gestation) both to ensure adequate prenatal care for the mother and unborn infant and to provide sufficient follow-up time to collect multiple antenatal study samples from the mother.